Initiation of non-invasive ventilation Initiation of invasive ventilation     Mean SD Mean SD p-value pH 7.23 0.13 7.23 0.12 0.79 PaO2 (kPa) 11.81 8.05 12.60 5.59 0.65 PaCO2 (kPa) 10.16 4.00 10.37 3.62 0.44 Lactic acid (mmol/L) 1.4 0.9 2.8 1.3 0.92 Base excess 2.3 7.9 2.9 6.8 0.40 HCO3- (mmol/L) 24.9 5.9 25.6 5.3 0.69 Oxygen saturation 0.89 0.08 0.94 0.06 0.01* Systolic blood pressure (mmHg) 120 26 107 25 0.02* Heart rate (min-1) 107 29 97 25 0.08 Respiratory rate (min-1) 30 9 25 10 <0.01* Temperature (°c) 37.3 1.3 37.1 1.2 0.40 Glasgow Coma Scale score 13 2 13 3 0.40

Table 3: Patients in the NIV failure group at the initiation of NIV and at the initiation of invasive ventilation. P-value less than 0.05 is marked with *.